A method of diagnosing a lubrication system of an engine includes controlling an oil pump with a control signal. The control signal is a command having a value for a desired lubrication fluid pressure from the oil pump for a current operating state of the engine. A processing unit compares the value of the control signal for the current operating state of the engine to a threshold control value for the current operating state of the engine. When the processing unit determines that the value of the control signal for the current operating state of the engine deviates from the threshold control value for the current operating state of the engine, the processing unit analyzes the value of the control signal to identify a fault in the lubrication system.